In recent years, as a compact camera, a camera using an image pickup device such as a CCD, has become common. In response to the popularity of such cameras, various compact imaging lenses using a relatively small number of lens elements and lens components have been developed.
One ultimate objective in camera development is for a camera that produces a finished image that is the same as the original scene viewed by the human eye. However, with compact cameras using an image pickup device, such as a CCD, it is difficult to produce a picture of a bright image which is the same as the image viewed by the human eye, even with high performance imaging capabilities, and the desired objective has not been achieved.
It is generally possible to take a bright picture of a short-range object by using stroboscopic lighting and recording techniques. However, distant objects are not adequately lit in stroboscopic lighting arrangements, and therefore images as bright as those seen by the human eye cannot be produced. This has also been proven by many photographers who have been unable to record beautiful night views. Furthermore, in the case of stroboscopic arrangements, there is also the problem that continuous imaging is difficult in order to secure the time required for stroboscopic exposures.
At the same time, the sensitivity of photographic films has recently been rapidly improved, and films with high sensitivity through super high sensitivity, such as ISO400, ISO800 or ISO1600, are commercially available. It is predicted that in the future, if a film with additionally higher sensitivity is sold in the marketplace, it will become possible to take a picture of a bright image which is the same as the image viewed by the human eye.
Compact imaging lenses for mounting in compact cameras that use photographic film are disclosed, for example, in Japanese Laid-Open Patent Applications H9-236746, H11-326756, 2000-321490, and 2001-124985. The lenses described in these applications satisfy conditions such as a short back focus, short length when retracted, and a small lens diameter, to some extent, and, for example, the lens described in Japanese Laid-Open Patent Application H9-236746 includes four lens components that, from the object side, have negative, positive, positive and negative refractive powers, providing a compact large aperture wide-angle lens with excellent performance when implemented in an F2.8, 28 mm focal length imaging lens.
However, it is known that the improvement of the sensitivity and graininess of a silver salt film has a so-called inverse proportional relationship, that is, as the film sensitivity is increased, improving brightness of an image, the image becomes grainier, creating a rough appearance that is unattractive. Additionally, the image becomes less sharp and problems in color reproduction occur, making it difficult to achieve the desired objective mentioned above of producing an image that looks the same as when the scene is viewed directly by the human eye.
As a result of many studies of the above problems by the inventor of the present application, the conclusion has been reached that it is possible to respond to the desired objective mentioned above by enhancing the film sensitivity to some extent so as to not cause any problem from the viewpoint of granularity while at the same time dramatically improving the brightness of the imaging lens used in photographic film cameras that use a silver salt photographic film.
Specifically, it is possible to reproduce an image that is the same as the image viewed by the human eye by using a silver salt photographic film with high sensitivity or with commercially available super high sensitivity in conjunction with an imaging lens having approximately 83 degrees or greater field angle and an f-number of approximately 2.0.